Prince Charles was today reported to have voiced fears over a shake-up of monarchy rules which would allow a daughter of the Duke and Duchess of Cambridge to take the throne.

The Prince of Wales is said to have taken aim at “rushed” changes to 300-year-old laws governing the line of succession.

Ministers announced in the summer that the regime, giving male heirs priority and barring Royals from marrying Roman Catholics, will be changed and backdated.

The move took on added importance last month when the couple announced that Kate is pregnant with their first child.

Charles is said to be worried that the overhaul could have “unintended consequences” and has not been thought through.

He is believed to have voiced critical questions last week in a meeting with one of Whitehall’s most senior mandarins.

Charles backs the reforms if they attract widespread support but he reportedly fears they could adversely affect the delicate relationship between the State and the Church of England as well as rules governing hereditary titles.

The Prince, who met with Cabinet Office permanent secretary Richard Heaton, apparently expressed his worries about what will happen if his grandchild is allowed to marry a Roman Catholic.

Church leaders believe a future heir who weds a Catholic will be required by canon law to raise their children in that faith.

A constitutional nightmare could ensue through a Catholic heir being barred from taking the monarch’s traditional role as Supreme Governor of the Church of England.

A source disclosed that the Prince was told the problem could be solved by negotiations with the Vatican – a solution he is said to have found “unsatisfactory and unconvincing”.

Charles, 64, is also said to have questioned the impact of changing the succession for other royal titles passed along the male line.

A spokesman for Buckingham Palace said: “Reforms are a matter for the Government. We have no comment to make.”